1. Field of the Invention
The present disclosure relates to a brake actuator.
2. Description of the Related Art
An air brake system for vehicles such as buses, trucks, trailers, other heavy vehicles or the like includes a brake shoe, and a drum assembly operated by an actuator assembly by selectively applying a compressed air.
General air brake actuator includes both a service brake actuator for applying a compressed air to operate a brake in a general running state, and a spring-type emergency brake actuator for operating the brake when the air pressure is released.
The emergency brake actuator includes a strong compression spring for applying a pressure to the brake when the air pressure is released.
This is also called a spring brake.
The air operated brake actuator may have a piston type or a diaphragm type.
In the diaphragm type, a brake actuator and two air-operated diaphragm brake actuators are generally disposed in a tandem vehicle shape, which includes an air operated service brake actuator for operating a general brake of a vehicle, and a spring brake actuator for operating an emergency brake or a parking brake of the vehicle.
The service brake actuator and the spring brake actuator include a housing which has an elastic diaphragm for dividing the inside of the housing into two distinguished fluid chambers.
Meanwhile, the piston brake actuator is operated in the same way as described above, except for the diaphragm, and the piston reciprocates in a cylinder for operating a parking brake of a vehicle.
In a general service brake actuator, the service brake housing is divided into a pressure chamber and a push rod chamber.
The pressure chamber is connected to a source of the compressed air to allow the fluid to flow, and the push rod chamber includes a push rod mounted thereto to connect to a brake assembly so that a compressed air is introduced into and discharged from the chamber by reciprocating the push rod into or out of the housing to lock or release the brake.
In a general spring brake actuator, the spring brake housing is divided into a pressure chamber and a spring chamber.
The pressure plate is located at a spring chamber between the strong compression spring and the diaphragm so that an opposite end of the strong compression spring is in contact with the housing.
As a known configuration, the actuator rod extends to the pressure chamber through the pressure plate and the diaphragm and also extends through a partition wall which separates the spring brake actuator from the service brake actuator.
An end of the actuator is connected the pressure chamber of the service brake actuator to allow a fluid to flow.
When the parking brake is operated, the pressure of the spring brake actuator is discharged from the pressure chamber, and the strong compression spring pushes the pressure plate and the diaphragm toward the partition wall between the spring brake actuator and the service brake actuator.
In this location, the actuator rod connected to the pressure plate operates the parking or emergency brake to be pushed so that the vehicle is forced not to move.
In order to release the parking brake, the pressure chamber is closed to the atmosphere, and the compressed air expands the pressure chamber, moves the diaphragm, and moves the pressure plate toward the opposite end of the spring brake actuator housing so that the compressed air is introduced to the pressure chamber of the spring brake actuator which compresses the strong compression spring.
However, in such a spring brake actuator, if a spring giving a great compression force is compressed, the pressure chamber increases its volume, and spring chamber decreases its volume, thereby increasing the pressure in the spring chamber.
In addition, a compressed air system for heavy vehicles is operated under a maximum industrial standard pressure, and thus the pressure generated in the spring chamber is further increased.
Due to the twinning pressure of the spring and the increased air pressure in the spring chamber, it is impossible to reach a maximum value at which the brake operates suitably.
Therefore, if the twinning pressure associated with the pressure of the spring and the generated pressure of the spring chamber approach a force applied by a maximum pressure, the brake may be not released, partially released in an unsatisfactory level, or very slowly released.